1. Field of the Invention
This invention relates to an air cut-off valve which finds application as a safety device for controlling the air intake of an engine.
2. Prior Art
An air cut-off valve is commonly employed to close the air intake line extending between the turbocharger and air intake manifold of a diesel or gas-fuelled engine. The valve is used to withhold air supply from the engine, in the event that it is sensed that hydrocarbons are entrained in the air. These valves are particularly needed, for example, in connection with the engines of a drilling rig, where there is a significant possibility that gas will escape from the well and cause the engines to continue running, even though the fuel supply has been closed off. The continued operation of the engines carries a high risk of causing the escaping gas to ignite.
The cut-off valve heretofore most widely used in this service in North America is disclosed in Canadian Pat. No. 587,457, issued to Oakes. This valve is described in some detail below because the present invention uses some of its concepts, but incorporates modifications with a view to overcoming some of its shortcomings.
The Oakes valve comprises a hollow, box-like, sectional housing having a greater length than width. This housing is formed using two hollowed-out halves or sections which are bolted together. An air inlet port extends through the upper end of the transverse upstream wall of one such section and an outlet port extends through the upper end of the downstream wall of the other section. The ports are linearly aligned. In use, the valve is inserted in the air line so that the ports and the chamber internal of the housing form part of the air flow path. The long housing extends well below the air line, for a purpose to be explained.
A valve member, comprising a stem and a gate carried thereby, is arranged to reciprocate longitudinally within the chamber. This valve member is movable between stored and operative positions. In the stored position, the gate is disposed in a storage cavity defined by the lower end of the chamber, out of the air flow path; the stem extends out the bottom of the housing. In the operative position, the gate is disposed across the ports, seals against the housing, and effectively blocks the air flow path.
A spring is provided to bias the stem and its attached gate from the stored position to the operative position. This spring is positioned around and along the stem and extends between the bottom wall of the housing and a shoulder on the valve member. When the valve member is locked by suitable locking means in the stored position, the spring is compressed. When the locking means is released, the spring expands and biases the valve member to the operative or blocking position.
The aforementioned releasable locking means comprises a lock-out cylinder which has a spring-loaded shaft that engages a recess in the valve stem, to lock the stem in the stored position.
In summary, the Oakes valve involves in concept the following features:
(1) a gate positioned in a sealed hollow, in-line housing, which gate is movable between a stored position, in which it is locked in a storage cavity formed by the housing out of the air flow path, and an operative position, in which it blocks and seals the air flow path; and
(2) a steam which carries the gate and biases it between the positions, said stem cooperating with mover means and locking means to provide the motion needed at the appropriate time.
The present invention also incorporates the aforementioned features. However, in applicant's view, the Oakes valve, while successful, has some shortcomings. The present invention involves significant structural and conceptual changes which have alleviated or done away with these problems.
One such problem associated with the Oakes valve is its size. It has a thickness of about 2-1/2" and a downwardly extending length of about 17", measured from the centreline of the air line. Since there is a scarcity of available space within the confines of an engine assembly, this bulkiness leads to problems of installation and accommodation.
The valve is necessarily thick in part because the coil spring is mounted around the stem, which arrangement follows from the use of a longitudinal drive.
That the valve is necessarily long follows from the incorporation of longitudinal movement of the gate and stem between longitudinally aligned storage and operative positions.
Another problem has to do with sealing of the stem. It protrudes out of the housing through an opening formed at the parting line of the housing sections. Tapping in at the parting line is necessary in order to be able to install a seal in a facile and inexpensive manner. However, it is difficult to so accurately machine the semi-circular openings in the housing sections that they are perfect matches, so that the seal, when mounted in the surfaces of the openings, fits properly and provides an air-tight seal between the stem and the housing.
Still another problem has to do with the positioning of the lock-out cylinder. In the Oakes valve, it is positioned in a plane perpendicular to the parting plane of the housing. This is done because it is easier to tap into the transverse wall of the housing than to tap in at the parting line. This arrangement further interferes with the objective of developing compactness as an attribute of the valve.
With this background in mind, it will be understood that there is a need for an air cut-off valve which is characterized by compactness, ease of sealing, and ease of manufacture.